He is German. He probably survived because he was lucky enough to remain fit enough to work, so wasn’t put to death, and didn’t catch any of the diseases that killed other camp inmates. He must have suffered terribly, especially when he discovered that everyone else who had been in the hidden house was dead. But he probably saw the fact that he had survived as something that should not be thrown away. He should make the best of the life he had been given, when so many others had not. He went on with life because it would have been something of an insult to those who died if he had not cherished what he had been given.